The present invention is related to an improved alkylation/transalkylation process which utilizes a dual reactor system employing dissimilar catalysts to produce a monoalkylaromatic product. More specifically, this invention involves the use of a solid phosphoric acid catalyst to catalyze the alkylation reaction, and an inorganic oxide bound crystalline aluminosilicate material to catalyze the transalkylation reaction. The invention also relies upon a synergism of the two reaction zones and two separation zones to produce a high purity monoalkylated aromatic product in higher yields than those attainable with only an alkylation reaction zone.
The alkylation of aromatics with an alkylating agent in the presence of an alkylation catalyst is a process well known for its ability to produce such monoalkylaromatic products as ethylbenzene, cumene, linear alkylbenzenes and so forth. Such monoalkylaromatic compounds are important chemical precursors in the production of detergents and polymers among others. Alkylation catalysts that are known to produce alkylaromatic compounds include the well known Friedel-Crafts catalysts; sulfuric acid, phosphoric acid, hydrofluoric acid, and aluminum chloride in either liquid or solid supported form. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized as alkylation catalysts in both a modified and naturally occurring form.
The use of a transalkylation reaction zone in conjunction with an alkylation reaction zone for the production of monoalkylaromatics is also well known. A transalkylation reaction zone employed in a process in conjunction with an alkylation reaction zone enables the alkylation reaction zone to be operated at higher conversion conditions due to the ability of the transalkylation reactant to convert the undesired polyalkylaromatic compounds produced by the higher alkylation zone conversion conditions into desired monoalkylaromatic compounds. Transalkylation catalysts that are known to have utility in the production of alkylaromatics from polyalkylaromatics include Friedel-Crafts catalysts such as sulfuric acid, phosphoric acid, aluminum chloride in either the liquid or solid supported form, and the like. Solid granular catalysts such as clays, zeolites, and amorphous materials have also been utilized as transalkylation catalysts.
A myriad of processing schemes employing an alkylation reaction zone, a transalkylation reaction zone, and a separation zone, and employing various product, feed, and intermediate product recycles are well known to produce monoalkylaromatic products. One drawback concerning known alkylation/transalkylation processes is the sometimes rapid deactivation of the transalkylation catalyst due to the presence of trialkylaromatic and higher boiling compounds in the transalkylation reaction zone feed. This rapid deactivation requires that frequent catalyst regenerations be performed, or that the transalkylation catalyst be frequently replaced. The replacement or frequent regeneration of a deactivated transalkylation catalyst can therefore become time-consuming and costly.
A drawback inherent to existing alkylation processes which utilize a Friedel-Crafts catalyst such as solid phosphoric acid or hydrofluoric acid as the alkylation catalyst is that many of these catalysts require a water cofeed and produce an extremely corrosive sludge by-product. The utilization of such high activity, sludge-producing catalysts in an alkylation process necessitates the operation of the process at high conversion once-through conditions which tend to produce greater amounts of unwanted di- and trialkylaromatics. The addition of a transalkylation reaction zone containing a stable, active transalkylation catalyst to such an alkylation process enables the conversion of the dialkylaromatics to monoalkylaromatics at high conversions without detrimentally affecting transalkylation catalyst life.